1. Field of the Invention
The present invention relates to a secondary battery and, more particularly, to a cap assembly for a secondary battery, which can prevent electrolyte from leaking out of the battery while providing safety and reliability of the battery.
2. Description of the Prior Art
Generally, the Li-ion battery uses lithium metal oxide as a positive active material and carbon or a carbon compound as a negative active material. Lithium salt dissolved in an organic solvent is used as the electrolyte via which the lithium ions move between positive and negative electrodes. Charging and discharging operations are realized while the lithium ions are moved between positive and negative electrodes.
FIG. 4 shows a cap assembly of a conventional Li-ion battery.
A cap assembly 6 is insulated from the can 4 by a gasket 8. That is, the upper end of the can 4 is crimped on the outer periphery of the cap assembly 6 with the gasket 8 interposed therebetween.
The cap assembly 6 comprises a safety plate 14 provided with a safety groove, a current control member 12 disposed on the safety plate 14, and a cap cover 10 disposed on the current control member 12. Attached under the safety plate 14 is a circuit breaker 18 with an insulator 16 disposed therebetween. The circuit breaker 18 is welded on a positive tab 20 so that it is coupled to a positive electrode of the electrode assembly 2.
In the conventional Li-ion battery structured as in the above, as the circuit breaker 18 is welded to the safety plate 14 with the insulator 16 interposed therebetween, the structure of the cap assembly is complicated. In addition, since the circuit breaker 18 and the insulator 16 are supported by the safety plate 14, the safety plate 14 may become deformed, causing the safety plate 14 and the circuit breaker 18 to malfunction.
Particularly, in the case of a cylindrical Li-ion battery, airtightness depends on a contacting area between the safety plate 14 and the gasket 8. However, in the conventional battery, an insufficient contacting area is obtained, negatively affecting airtightness.